2010 YTD - 2011YTD (NPD numbers)
June was pretty astonishing for Xbox360 in the US and it may indeed exceed 2010 for the rest of the year too, but the next couple of months is where it could really lose ground, that being said we all expected that to start with June but look how that turned out.
July 2010 was 440k, and they HAVE to be down, but if these deals continue into July they could pull 350k, so only a 100k drop. Then if they drop price in August they'll be up on last years 350k, if they don't they'll likely be down 50 to 100k.
In which case they will 100% cut in Sep with Gears, and that will be rapidly up YOY (480k), for the rest of the year, MS will be up. I don't think their claim they will be #1 WW is made lightly, they wouldn't keep repeating it unless they were sure.